The invention relates to a method of melting glass in a melting furnace having a melting tank with a tank bottom and furnace superstructure with a furnace crown, which has:
a preheating zone, a melting zone, a refining zone with a refining bank raised above the rest of the floor and an homogenizing zone, arranged lengthwise behind one another between the charging end for the glass raw materials situated near a first end wall and a second end wall, whereby PA1 at least one dividing wall protruding downwards from the crown is provided inside the furnace between the first end wall at the charging end and the melting zone to retain the flame radiation, whereby a flow path for the waste gases coming from the burners is provided so that the glass raw materials in the preheating zone can be heated, and PA1 the melting zone, the refining zone, several burners and the homogenizing zone are in a common combustion chamber in the superstructure, the two ends of which are defined by the last dividing wall and the inside face of the second end wall, and PA1 a first flow path of the glass, with a horizontal component of length "L1", is formed between the inside face of the first end wall and the vertical center line (E) of the aforementioned last dividing wall before the refining zone, and PA1 a second flow path of the glass, with a horizontal component of length "L2", is formed in the aforementioned combustion chamber between the vertical center line (E) of the aforementioned last dividing wall and the inside face of the second end wall, and whereby PA1 a current is produced from the melting zone in the direction of the charging end and a counterflow bottom current is produced by means of the creation of a temperature gradient in the glass melt through the addition of heating energy to the glass bath by means of burners installed in the combustion chamber. PA1 1. they have an adverse effect on the investment and the furnace operating costs, since a suitable transformer is required, and expensive electrical energy is used, and PA1 2. they produce an upwardly moving convection current in the glass melt, which is opposed to the current coming from the melting zone, and so do not assist this current. PA1 the ratio of the length of the horizontal component of the second flow path of the glass melt in the combustion chamber ("L2") to the combined lengths of the horizontal components of the first and second flow paths of the glass melt ("L1"+"L2")is chosen to be at least 0.5, and PA1 at least the greater part of the heating energy is introduced into the glass melt in the melting zone, and PA1 a preheating zone, a melting zone, a refining zone with a refining bank raised above the rest of the floor and an homogenizing zone, arranged lengthwise behind one another between the charging end for the glass raw materials situated near a first end wall and a second end wall, whereby PA1 at least one dividing wall protruding downwards from the crown is provided inside the furnace between the first end wall at the charging end and the melting zone to retain the flame radiation, whereby a flow path for the waste gases coming from the burners is provided so that the glass raw materials in the preheating zone can be heated, and PA1 the melting zone, the refining zone, several burners and the homogenizing zone are in a common combustion chamber in the superstructure, the two ends of which are defined by the last dividing wall and the inside face of the second end wall, and PA1 a first distance "L1" is formed between the inside face of the first end wall and the vertical center line (E) of the aforementioned last dividing wall before the melting zone and the refining zone, and PA1 a second distance "L2" is formed in the aforementioned combustion chamber between the vertical center line (E) of the aforementioned last dividing wall and the inside face of the second end wall. PA1 In order to achieve the object of the invention, a furnace according to the invention is characterized by PA1 the ratio of the second length "L2" in the combustion chamber to the combined lengths ("L1"+"L2") between the first and second end walls is a minimum of 0.5, PA1 the majority of the burners are installed in the area of the refining zone in front or upstream of the refining bank in the part of the melting zone where the glass bath is deeper, and PA1 the charging end of the melting tank is not electrically heated.
A prior art method and the equipment for the practice of the method are disclosed by U.S. Pat. Nos. 4,882,736, 4,852,118 and 4,789,990. The main objective is to reduce the nitrogen oxide and dust content in the waste gases and simultaneously to increase the thermal efficiency. A main characteristic of this is the production of a temperature gradient in the glass melt, where the temperature increases between the charging end and the refining zone, as a result of the extremely intense heating of the glass melt by fossil fuel burners in the melting zone, which produces a current flowing from the melting zone to the charging end. By means of a further measure, the waste gases from the burners are transported above the contents of the furnace to the charging end, where they are passed through two lateral flue outlets to heat exchangers and then to a waste gas stack, and in conjunction with the current path produced by the internal dividing walls, the waste gases pass over the glass raw materials floating on the glass bath surface, and, so doing, transfer significant quantities of heat to the raw materials, which promotes and accelerates the melting. The waste gases therefore flow basically in counterflow to the glass raw materials, which consist of batch and/or cullet.
For this purpose, the fossil fuel burners are installed in the superstructure of a combustion chamber in which the melting zone, the refining zone which has a very shallow bath depth, and the homogenizing zone, which immediately follows the refining zone, and which has a significantly deeper bath depth, are also situated. The homogenizing zone leads to a throat for the glass melt in the direction of a working end. A number of the fossil fuel burners are installed above the very shallow refining zone, but this does not preclude the installation of further burners in front of a further dividing wall, which forms the end of the aforementioned combustion chamber in the direction of the charging end. The part of the furnace in front of this dividing wall in the direction of flow is described as the preheating zone. The complete length of the furnace is determined by the length of the preheating zone, the melting zone, the refining zone and the homogenizing zone.
In the prior art solution the length of the aforementioned combustion chamber, defined as being from the vertical center line of the upstream dividing wall to the inside face of the downstream end wall, is much less than 50% of the distance between the inside face of the end wall at the charging end and the inside face of the end wall at the other end of the furnace in the area of the throat. If the drawing is to scale, then the aforementioned combustion chamber with the fossil fuel burners, the melting, the refining and the homogenizing zones takes up approximately 1/3 of the total length of the furnace, while the preheating zone covers the remaining 2/3 of the length. This length ratio causes significant heat losses along the flow path of the glass in the preheating zone, so that the glass currents no longer transport sufficient heat in the direction of the charging end of the furnace. However, very large amounts of heat are required in exactly this area to heat the glass raw materials.
In order to solve this problem for equipment built according to the prior art solution, additional electrodes are installed in the bottom area of the charging end, by means of which the glass melt in the charging end is heated electrically in order to prevent the temperatures in this area from falling below a certain level, or even to prevent the glass melt from solidifying. However these electrodes are disadvantageous in that